The following provides a general introduction, and includes an extract from Wikipedia. Please see http://en.wikipedia.org/wiki/Lighting#Fixtures.
Lighting fixtures come in a wide variety of styles for various functions. Some are very plain and functional, while others are pieces of art in themselves. Nearly any material can be used, so long as it can tolerate the heat and is in keeping with safety codes.
Lighting types are classified by intended use as general, localized, or task lighting, depending largely on the distribution of the light produced by the fixture.
General lighting fills in between the two and is intended for general illumination of an area. Indoors, this would be a basic lamp on a table or floor, or a fixture on the ceiling. Outdoors, general lighting for a parking lot may be as low as 10-20 lux (1-2 foot-candles) since pedestrians and motorists already used to the dark will need little light for crossing the area.
Task lighting is mainly functional and is usually the most concentrated, for purposes such as reading or inspection of materials. For example, reading poor-quality reproductions may require task lighting levels up to 1500 lux (150 foot-candles), and some inspection tasks or surgical procedures require even higher levels.
Task lighting may include a glare norm. Glare herein indicates over-illumination. A first type of glare occurs when light that is reflected on furniture is too bright. This first type of over-illumination may occur indoors when light levels exceed for instance 500 lux for incidental lighting, exceed 800 lux for general office use or exceed 1,500 lux for special purpose use. Note, the midday sun provides about 32,000 to 100,000 lux depending on latitude, time of year and cloud cover. Another type of glare involves direct lighting. To prevent this second type of over-illumination indoors, brightness may for instance be limited to 1000 Cd/m2 outside an angle of about 60 degrees with respect to a normal (perpendicular) line. Full-width half-maximum is defined as the divergence angle at half of the maximum light output intensity of a luminaire.
Localized lighting is mainly decorative, intended to highlight pictures, plants, or other elements of interior design or landscaping.
Methods to achieve the above lighting types include uplighting, downlighting, frontlighting and backlighting.
Downlighting is most common, with fixtures on or recessed in the ceiling casting light downward. This tends to be the most used method, used in both offices and homes. Although it is easy to design it may cause problems with glare and excess energy consumption due to a large number of fittings.
Uplighting is often used to bounce indirect light off of the ceiling and back down. It is commonly used in lighting applications that require minimal glare and uniform general illuminance levels. Uplighting (indirect) uses a diffuse surface to reflect light in a space and can minimize disabling glare on computer displays and other dark glossy surfaces. It gives a more uniform presentation of the light output in operation.
Frontlighting is also quite common, but tends to make the subject look flat as its casts almost no visible shadows. Lighting from the side is the less common, as it tends to produce glare near eye level. Backlighting either around or through an object is mainly for accent.
Lighting design as it applies to the built environment, also known as ‘architectural lighting design’, is both a science and an art. Comprehensive lighting design requires consideration of the amount of functional light provided, the energy consumed, as well as the aesthetic impact supplied by the lighting system. Some buildings, like surgical centers and sports facilities, are primarily concerned with providing the appropriate amount of light for the associated task. Some buildings, like warehouses and office buildings, are primarily concerned with saving money through the energy efficiency of the lighting system. Other buildings, like casinos and theatres, are primarily concerned with enhancing the appearance and emotional impact of architecture through lighting systems. Therefore, it is important that the sciences of light production and luminaire photometrics are balanced with the artistic application of light as a medium in our built environment. These electrical lighting systems should also consider the impacts of, and ideally be integrated with, daylighting systems.
As indicated above, some lamps provide task light, such as overhead TL luminaires. Other lamps provide general light, for instance a chandelier. As providing two different lamps for the two different lighting types is expensive, it would be advantageous if both light types could be combined in a single luminaire.
WO-2006/043196-A1 provides a device for electrically controlling shaping of a light beam. The device includes primary optics to shape a light beam from a light source. Adjacent to the primary optics, the device includes an electrically controlled scattering element. The scattering element may comprise polymer dispersed liquid crystals (PDLC) or liquid crystal (LC) gels. Secondary optics are provided adjacent to the scattering element to shape the scattered, diffracted or refracted light beam coming from the scattering element. However, the control of the light beam is limited to influencing the full-width half-maximum divergence angle.